Typical M20C speeds (TAS)

[Hank]

Depending on altitude the 20J is about 10 knots faster, the E and F are within one knot and the C falls off a little more as altitude goes up.  Also depends on how rich you want to run and fuel flow.  I tend to fly LOP so lose a little speed for the better economy.

 

This matches my experience, except for the last sentence. My C will not run smooth LOP. Does anyone? Yes, I've tried a little carb heat, and I always fly with the throttle pulled back enough to move the MP needle, hoping for turbulent flow through the carb and improved fuel atomization & mixing.

[nels]

Has this exercise been done for the M20 E and J model?? It is interesting to see what the difference in performance can be from plane to plane.

How about an E model comparison and after that one cools off then a J model comparison. Or maybe that should be accomplished on three different threads?

[RangerJim]

Go to the MAPA website homepage and you will easily find real world climb and cruise analyses utilizing 4 way GPS runs for many of the various models from the C forward.  Matches Lood's analysis very well.

 

I concur with those that find the M20C to be a fine combination of speed, economy, and utility for the price.  Now if I could just get those Rockets off my mind.

[rbridges]

I'd like to see an E model with a 201 cowling.  I know there are a few around, and I bet they are smokin' fast.  

 

Anyway, back to the OPs question.  I would bet on 135knots or so in a stock C model.

[jetdriven]

I'd like to see an E model with a 201 cowling.  I know there are a few around, and I bet they are smokin' fast.  

 

Anyway, back to the OPs question.  I would bet on 135knots or so in a stock C model.

 

I've ridden in a M20E with the 201 cowl and windshield. It is every bit as fast as a J, perhaps a couple knots more.

[PTK]

The only way to actually verify TAS is a 3-track GPS verified groundspeed put into an NTPS excel formula. Further, in the M20J, the CAS is 2 knots less than IAS, before corrections for density altitude. PM me for the excel spreadsheet.

+1

Have you done this Byron? What TAS have you arrived at using this method? I wonder how different it would be from doing a real world NSEW and taking an average.

Doug Gray's paper is an excellent read on this if anyone is intetested.

http://contrails.free.fr/temp/TAS_FNL4.pdf

[jetdriven]

It all depends on density altitude. We can count on a solid 149-150 KTAS between 4-8K at 15-25 degrees LOP, and 155 80 ROP.   The air race speed is 167-168 KTAS, and that was done at a 3,000 density altitude and full throttle, ~150 ROP.

[Hector]

This thread inspired me this morning to go out and do a 4 way GPS run in my 67C. It has a few speed mods but not the 201 cowling or windshield (does have a one piece windshield). Climbed to 7500, WOT which yielded 23MP, 2400 RPM, leaned till it started running a little rough then enriched till smooth. OAT was 6 C. Average of 4 way GPS run was 146 (fuel flow 9.8). Repeated again but this time enriched mixture for best power. Average of 4 way GPS run was 148.5. (Fuel flow 10.6).

[rob]

Again, a 4 way GPS run is not a good way to accurately measure TAS.

[jetdriven]

Neither is 2400 RPM. raising it to 2500 RPM is worth another 2-3 knots, and according to Jerry Manthey, 6 knots.

[Lood]

Again, a 4 way GPS run is not a good way to accurately measure TAS.

 

Hi Rob, I also did the 4-way GPS run on with my previous engine - as described in the Mapalog flight review articles. I plan to do another with my new engine to see if there's a difference and I would really like to know the correct way, if the above mentioned is not accurate.

Would you mind explaining the more accurate way?

[rob]

http://www.eaa62.org/technotes/speed.htm

Plug your numbers in there. Alternatively, google GPS True Airspeed calculator and you'll find other examples and explanations of why the math is required.

Basically the reason is that there will be an affect from winds aloft, and the math will eliminate that.

[Jerry 5TJ]

Here is an update on speeds of my basically stock M20C.

Speeds are GPS 4 direction averages.

I flight plan 140 knots. 

 

[phecksel]

My old C would see 150-153, but it had a LOT of mods

 

Here's a couple of hints, move the CG to the back of the envelope.  When I raced, I always carried a container of used wheel weights, tool box, and anything else I could in the baggage compartment.  Being 6'4" i could also cruise with the seat slid all the way to the back seat.  One final hint, and you can argue all day long about the OWT of the step, but I would try to overshoot final altitude by 100' or so, let the airspeed stabalize, and then decend down to final altitude.  More often than not, I would see an increase of 5 kts.

[Hector]

Your numbers are very close to mine. At 7500 feet, 2400 RPM, and 22in I get 142 kts on a 4 way speed run. I have a few mods, but not the 201 windshield.

[Jerry 5TJ]

Hi Rob, I also did the 4-way GPS run on with my previous engine - as described in the Mapalog flight review articles. I plan to do another with my new engine to see if there's a difference and I would really like to know the correct way, if the above mentioned is not accurate.

Would you mind explaining the more accurate way?

 

The 4 way GPS method works fine so long as you fly 4 orthogonal ground tracks, which is easy with the GPS.

Wolfgang Polack's calculator from the EAA is for use with data from three magnetic headings flown 90 degrees apart.

Both methods will give the same TAS.   

Just don't fly four orthogonal headings and average those readings as the results will be in error and the magnitude of the error will rise with the wind component.   Even then the numbers will be quite close if the wind is a small % of the TAS and even closer if one of your headings lies directly into the wind.      

When the wind aloft is zero all this becomes moot and a 1 direction run (your choice of heading, track or a gentle curve) give the same TAS = Ground Speed.

 

Three other factors in accurate TAS measurements --

First -- The time required for the plane to accelerate to its steady-state velocity after a 90 degree turn: I find several minutes of careful flying in calm air will show several knots higher than in the first minute after the turn.  

Also -- Flying smoothly and holding altitude  + 20 feet is also required as the Mooney will pick up several knots in a 50 fpm descent.

And -- the plane is faster in calm air, too, as even small control inputs noticeably slow the plane. 

 

Our 40 - 50 year old ASI systems give different results (often by far) than the externally-referenced GPS numbers.   My own M20C is way faster than average -- if I believe what the airspeed indicator says.  For instance, at 7500' I saw a TAS of 143 knots per GPS (4 ortho tracks averaged) and the IAS was 160 mph which is 181 mph TAS by calculation (30.15", 7C) or 157 KTAS:  A great bragging figure, but not real, alas. 

 

 

 

 

[Wildhorsesracing]

'62 M20C

 

I flightplan 135 kts 10 gph and usually average ~140 kts @ 9+ gph.

 

Mods: 1 pc belly and rotated brake calipers.

[BigTex]

'62 M20C

I flightplan 135 kts 10 gph and usually average ~140 kts @ 9+ gph.

Mods: 1 pc belly and rotated brake calipers.

+1... Same here

[Lood]

Thanks Jerry. Will see if I can get around to do a speeds test this coming weekend.

[scottfromiowa]

135-140- knots in a C is pretty darn good. 150+ knots well I would like to see that in a legitimate test at 5000-8000 feet. By legitimate I mean flying three cardinals and plugging into formula. If you are just doing runs and checking ground speed this isn't giving a representative speed of your plane...except on a given day with a given wind with a given power at a given altitude.

If some get angry that I challenge your assertion to your C's speed...O.K., but I call shenanigan's...again.

[phecksel]

The 4 way GPS method works fine so long as you fly 4 orthogonal ground tracks, which is easy with the GPS.

Wolfgang Polack's calculator from the EAA is for use with data from three magnetic headings flown 90 degrees apart.

Both methods will give the same TAS.   

.  

I remember plugging some numbers into an online formula and coming up with 148 or 149 and wondering how that compared to the 152-153 I believed I flew.  smooth air was a LOT better for speed, little bumps would start scrubbing speed off pretty quick.  Like I said, it was an exceptionally fast C.  IAS was typically 165, and decents from higher altitudes were challenging as I bumped right into red line without any effort.

 

As i said above, overshoot your altitude and decend down to final altitude would arrive at stabilized speed much faster than waiting for the plane to accelerate to final speed... this is what people believe is the "step".  Get that CG rearward and stop fighting the drag.

[scottfromiowa]

Ours can't do 150, Scott, but it can do 147. WOT, 2500 RPM, 8500 feet density altitude, max power mixture. It is lightly antennaed, has a new roller tappet engine, Powerflow exhaust, and brake caliper rotation mod. Otherwise stock.

The thing is, though, that with the PowerFlow it takes noticably more fuel to do it. It was a 142 knot bird prior to being re-engined and PowerFlowed.

How much more fuel Jim? Break the code for me. What does the "max power mixture for your C" equate to in Gallons per Hour fuel flow? We can "make" our planes fly fast with the dumping of fuel, but it would be good to go to a specific altitude (say 7500) set a specific power 2500RPM max MP you can get (those with ram air get a little more here E/F) AND a specific fuel flow...say 10GPH and then do the three speed runs in level cruise and compute it. Then except for density you have apples to apples. Do most fly at max power mixture cross country? I sacrifice some speed for fuel flow...Maybe also agree on the max power mixture in GPH Fuel Flow (we talking 100 ROP?='s what GPH fuel flow and do this speed comparison too.

There is flat out speed and there is real world cruise speed...What is REALLY being compared here?

[scottfromiowa]

My book speed and fuel burn at 7500 feet 2500RPM 23"MP at 9.9GPM is 176MPH at 2575lbs and 180MPH at 2200lbs. I will go get these numbers and report back on my 66 M20E. My predication...NOT 150+Knots...

[scottfromiowa]

Remember in January of this year original poster asked "what speed could be obtained at a fuel flow of 10GPH?"

[scottfromiowa]

I can't speak for the others, Scott, but I am reporting what I would consider to be max cruise speed here. Of course you could run the RPM up to 2700 for a little more speed (and fuel flow) but I don't think that many people like to run there. At least I don't, primarily due to the noise level. Max power is 80 dF ROP, but I tend to use 125 dF ROP instead when I want to go fast just to provide a bit more cooling margin since we don't have an engine monitor in the C.Unfortunately it also doesn't have fuel flow equipment, so I can't report cruise fuel flows before and after. What I can tell you is that we have owned the plane since 1982, so we know it well. The PowerFlow and roller tappet engine went on in 2007, I think. WOT operating technique did not change but what was previously a set-your-clock-by-it 10 GPH "block" fuel flow plane is now more like a 11 or perhaps 11.5 GPH hour "block" average plane.FWIW, my J is only 158 knot plane under the same conditions. I'm not exaggerating anything here. No reason to.Jim

Thanks Jim. I will also do at "max" for 7500 which is a fuel flow of 10.8 (book) (I will call it 11GPH) I just don't fly ROP, but it looks like the powerflow essentially increases fuel flow by about 1GPH. I can do that with mixture and see what a 50LOP (10GPH) speed is and at 11GPH which I think will be about 100ROP. Book speeds for M20E at 7500 (max) increase by 7MPH for 1GPH increase.